Evaluating Quinone Redox Chemistry for CO₂Capture in Aqueous Solvents under Flue Gas Conditions

Electrochemical quinone-mediated CO₂ capture offers a promising strategy for mitigating global carbon emissions. However, many quinone studies are conducted in organic solvents, and the CO₂-quinone redox chemistry is less explored under application-relevant conditions, such as aqueous solvent and flue gas concentration. To address this gap, we investigated the effect of aromaticity and the electronic structure of different quinones on their CO₂ binding and release under aqueous flue gas conditions. Cyclic voltammetry studies revealed that quinones with smaller aromatic systems exhibited stronger CO₂ binding, which was attributed to their higher nucleophilicity. However, in CO₂ capture and release studies, the quinone with the highest binding constant did not lead to the best capture performance. Among the quinones studied, 1,2-naphthoquinone-4-sulfonic acid (NQS), an intermediate-sized quinone, exhibited the highest performance. At 10 mA/cm² under a 20% CO₂ feed, NQS achieved a CO₂ release rate of 227 μmol/h, maintaining 45% electron utilization over 16 h. Electrochemical impedance spectroscopy analysis shows that NQS maintains a similar charge-transfer resistance during both CO₂ capture and release, which is consistent with its superior performance relative to the other quinones studied. These findings reveal a clear structure–property relationship and highlight the need for an optimal balance between CO₂ binding strength and redox reversibility.